Shock absorber support arrangement

ABSTRACT

In a shock absorber support arrangement including a support bearing structure, a hydraulic cylinder which includes a piston and a cylinder which is hydraulically coupled to the support bearing structure, the support bearing structure having a housing including a force transmission means having a chamber which is filled with a hydraulic medium and is in communication with the cylinder, the hydraulic cylinder being connected to the support bearing structure so as to be axially movable over a certain extent as a result of friction forces effective between the piston and the cylinder wherein the load forces of the piston are transmitted via the hydraulic fluid in the cylinder and the support bearing structure directly to the force transmission means.

This is a Continuation-in-Part Application of International ApplicationPCT/EP2003/012615 filed Nov. 12, 20003 and claiming the priority ofGerman application 102 59 532.1 filed Dec. 19, 2002.

BACKGROUND OF THE INVENTION

The invention relates to a shock absorber support arrangement includinga hydraulic cylinder.

In hydro-pneumatic spring-damper systems the customary spring-damperarrangement is a hydraulic cylinder. A gas spring accumulator performsthe functions of the spring effect and of bearing the operating load,and the damping is provided by a throttle diaphragm in an overflow linebetween the hydraulic cylinder and gas spring accumulator. A dampersystem of such a design is known, for example from German laid-openPatent Application DE 199 32 868.

Such hydro-pneumatic spring-damper arrangements may completely fulfillthe tasks of conventional spring damper systems in principle, therequirements in terms of installation space being somewhat morefavorable than in conventional spring damper systems. Thesehydro-pneumatic spring-damper arrangements also provide a very simpleway of implementing active damping of the vehicle body movements orwheel movements in a vehicle by adding hydraulic fluid to the workingspace of the hydraulic cylinder or discharging it therefrom.

However, a basic problem of such arrangements is the unavoidablefriction of the hydraulic actuator in the hydraulic cylinder. Owing tothe operating loads to be borne when used in a passenger car it isvirtually impossible to achieve cylinder friction values below 100 to200 N. However, this adversely affects comfort.

It is known to use soft head bearings in order to improve the comfort,as illustrated in FIG. 1. There are however narrow configuration limitsbecause of the basic load and the service life requirements so that itis virtually impossible to implement rigidity values of the bearings ofless than 1000 N/mm.

DE 196 29 959 A1 discloses a device of the generic type. A supportbearing of a vibration-damping element has a hydraulic cylinder which iscoupled hydraulically to the support bearing, with the support bearinghaving a housing which is filled completely with hydraulic medium.

The object of the present invention is to provide a shock absorbersupport, in particular a hydropneumatic spring-damper system whichincreases the ride comfort of a vehicle.

SUMMARY OF THE INVENTION

In a shock absorber support arrangement including a support bearingstructure, a hydraulic cylinder which includes a piston and a cylinderwhich is hydraulically coupled to the support bearing structure, thesupport bearing structure having a housing including a forcetransmission means having a chamber which is filled with a hydraulicmedium and is in communication with the cylinder, the hydraulic cylinderbeing connected to the support bearing structure so as to be axiallymovable over a certain extent as a result of friction forces effectivebetween the piston and the cylinder wherein the load forces of thepiston are transmitted via the hydraulic fluid in the cylinder and thesupport bearing structure directly to the force transmission means.

The invention provides for active suspension systems which are of simpledesign and which are based in particular on hydropneumatic systems to beprovided with a high level of comfort since a central problem ofhydropneumatic systems, the disruptive influences of friction in thehydraulic cylinder, can be essentially eliminated or at least greatlyreduced.

When the vehicle support arrangement according to the invention is usedas a head bearing it is possible to prevent or attenuate disruptivecharacteristics of the actual force-transmitting component.

The invention will become more readily apparent from the followingembodiment thereof on the basis of the accompanying drawings

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a conventional hydropneumatic spring-damper system with asoft head bearing,

FIG. 2 shows the change in force as a function of the excursion/springcompression given sinusoidal excitation under the influence of afriction value of 150 N,

FIG. 3 shows the spring-damper changes in force given sinusoidalexcitation according to FIG. 2,

FIG. 4 is a basic representation of a preferred hydraulic supportbearing,

FIG. 5 shows schematically a preferred hydropneumatic spring-dampersystem with a first preferred support bearing,

FIG. 6 is a schematic representation of a preferred hydropneumaticspring-damper system with a second preferred support bearing,

FIG. 7 shows the change in force as a function of the excursion/springcompression given sinusoidal excitation under the influence of afriction value of 150 N with an arrangement according to the invention,

FIG. 8 shows the spring-damper changes in force given sinusoidalexcitation according to FIG. 7,

FIG. 9 shows the excursion values of the head bearing or cylinderaccording to FIGS. 7 and 8,

FIG. 10 is a basic representation of a preferred configuration of asupport bearing,

FIG. 11 is a basic representation of a further preferred configurationof a support bearing with extension stops and compression stops, and

FIG. 12 is a basic representation of a further preferred configurationof a support bearing with longitudinal guide means.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates a known hydropneumatic spring-damper system. Ahydropneumatic spring-damper system includes as a vibration-dampingelement a hydraulic cylinder 1 with a piston 6 which can move up to anddown from in the interior of the hydraulic cylinder 1. A gas springaccumulator 2 performs the functions of the spring effect and of bearingan operating load, said gas spring accumulator 2 being connected to thehydraulic cylinder 1 via an overflow line 4 through which a hydraulicmedium can be exchanged between the hydraulic cylinder 1 and the gasspring accumulator 2. The damping is implemented by a throttle 5 in theoverflow line 4 between the hydraulic cylinder 1 and gas springaccumulator 2. A support bearing 3 with a spring stiffness C_(L) isarranged at the body support end.

With a spring compression by a distance Xe, a force F acts on the piston6 which is forced upward in the direction of action of the force by adistance Xz, while the hydraulic cylinder 1 experiences excursion ΔX.Owing to the operating load to be borne, for example that of a vehicle,the unavoidable friction of the piston 6 in the hydraulic cylinder 1leads to losses of comfort. One possibility for compensation is toreduce the spring stiffness C_(L) of the support bearing 7. However,there is little room for maneuver in terms of the configuration owing tothe high basic load represented by the vehicle and the existing servicelife requirements. For this reason, spring stiffnesses C_(L) with valuesof less than approximately C_(L)=1000 N/mm are virtually impossible toachieve.

FIG. 2 illustrates effects of the frictional forces for a sinusoidalexcitation of spring compression of a conventional hydropneumaticspring-damper system with a spring stiffness of a support bearing ofapproximately C_(L)=1200 N/mm and a piston friction of 150 N. In FIG. 3,the associated spring-damper change in force (dF_Zyl [N]) is illustratedin comparison with the spring component (dF_elast). It is apparent thatwhen there is reversal of movement of the piston 6 jumps in force of 200to 400 N may occur and these have a very disruptive effect which reducescomfort particularly at lower spring compression values. The force ofthe piston changes virtually spontaneously by up to twice the frictionalforce of the piston 6 especially when there is reversal of movement. Theflexibility of the support bearing 7, in this case of a head bearing, istoo low to be able to effectively smooth or even out these changes inforce due to friction.

The principle of the solution according to the invention is outlined inFIG. 4. Only a support bearing 7 is represented in detail; the otherarrangement (not illustrated) corresponds largely to the systemillustrated in FIG. 1. Here, a spring-damper system is provided as aspring-damping element. The support bearing 7 has defined hydraulic,elastic and possibly damping properties and is hydraulically coupled toa hydraulic cylinder 1 (not illustrated in the figure). The body of thesupport bearing 7 preferably has defined stiffness properties.

A hydraulic active area A_(L) is arranged between the support bearing 7and hydraulic cylinder 1. The support bearing 7 has a housing 10 with aspring stiffness C_(L). The housing 10 is preferably filled completelywith a hydraulic medium. A pressure p is present inside the housing 10.Since the support bearing 7 is hydraulically connected to the workingspace of the hollow cylinder 1, p is also the pressure of the workingspace of the cylinder 1.

The hydraulic coupling of the support bearing 7 and hydraulic cylinder 1means that the actual functions of the support bearing 7, bearing theload and compensating lengths, can be separated. The hydraulic mediumpresent is utilized to support the load. For a given hydraulic activearea it is thus possible to ensure that the support bearing 7 fulfillsits bearing function for any necessary and customary loading. The lengthcompensation, i.e. longitudinal flexibility of the support bearing 7,can now be implemented by means of rubber elements or steel springelements. Since the basic load is accommodated by the hydraulic fluid,the tuning bandwidth is not limited by configuration restrictions. Thespring stiffness of a support bearing according to the invention cantherefore be significantly less than in a conventional support bearing 7according to FIG. 1. For example, the previous limiting value withconventional support bearings of typically at least C_(L)=1000 N/mm canbe reduced to values of around 50 N/mm, preferably around 25 N/mm.

The effective area A_(L) between the hydraulic cylinder 1 and thesupport bearing 7 is preferably constant when the hydraulic cylinder 1and/or the support bearing 7 experiences excursion. As a result of thearrangement according to the invention, a considerable improvement incomfort can be achieved. However, even if the hydraulic active area isvaried, at least an improvement in comparison with the known systems canbe obtained. An essentially constant hydraulic active area A_(L), i.e.one which is neutral in terms of area, is favorable in order to makeavailable sufficient excursion travel for “smoothing out” the frictionin the hydraulic cylinder 1.

If, for example, during the spring compression the support bearing 7 issubject to an excursion of ΔX, this is counteracted by the springstiffness C_(L) and a hydraulic opposing force acting on the hydrauliceffective area A_(L) on the support bearing 7 a bearing force K counterto the excursion ΔX:K=C _(L) ·ΔX+A _(L)·(ΔX)·P

Owing to the limited space in the support bearing 7 it is necessary atthe same time for a transfer volume flow S_(L) of the hydraulic mediumto flow into the hydraulic cylinder through the hydraulic effective areaA_(L):$S_{L} = {A_{L} \cdot \left( {\Delta\quad X} \right) \cdot \frac{{\mathbb{d}\Delta}\quad X}{\mathbb{d}t}}$

It is particularly favorable to adapt the hydraulic effective area A_(L)approximately to the effective hydraulic working faces of the hydrauliccylinder. Furthermore it is favorable at the same time to make themechanical spring stiffness C_(L) of the support bearing relativelysmall. These measures make it possible for the support bearing 7 to“smooth out” changes in the frictional force of the piston 6.

The hydraulic medium can escape from the hydraulic cylinder 1 into a gasspring accumulator 2 (see FIG. 5). The support bearing 7 is preferablyarranged hydraulically in parallel with the gas spring accumulator 2.

FIG. 5 illustrates a first preferred arrangement according to theinvention. The support bearing 7 is embodied as an ellipsoid body.Otherwise the arrangement corresponds largely to the basic outline inFIG. 1. The supporting body 7 is arranged axially on the hydrauliccylinder 1, in the longitudinal direction of the hydraulic cylinder 1.The support bearing 1 forms a head bearing of a hydropneumaticspring-damper. It is also possible to operate such an arrangementactively and to use a hydraulic pump (not illustrated) so thatadditional hydraulic medium can be pumped into the arrangement orhydraulic fluid can be discharged from it.

FIG. 6 illustrates a second preferred arrangement according to theinvention. Here, a folding bellows is used as the support bearing 7instead of an ellipsoid body. This arrangement has the particularadvantage that the hydraulic active area A_(L) remains neutral in termsof area during movements of the piston 6 or spring compression andspring extension movements. An elastomer can be used as the material forthe housing. A further favorable and particularly corrosion-resistantalternative is a metal bellows.

FIGS. 7 and 8 clearly show the improvements in comparison with FIGS. 2and 3 for a conventional system according to FIG. 1.

In FIG. 7, the effects of the frictional forces for sinusoidal springcompression excitation of a conventional hydropneumatic spring-dampersystem with a spring stiffness of a support bearing 7 according to theinvention of approximately C_(L)=25 N/mm and a piston friction of 150 Nare illustrated. FIG. 8 illustrates the associated spring-damper changein force (dF_Zyl [N]) in comparison to the spring component (dF_elast).It is apparent that when there is a reversal of movement of the piston 6virtually no further force jumps are observed. When there is a reversalof movement, the change in force according to FIG. 7 is continuous witha gentle transition into an opposing movement.

The resulting time/force profiles in FIG. 8 are harmonic and smooth andshow that adverse effects on comfort in comparison with the conventionalsystem can be avoided.

FIG. 9 shows the excursion values Xz of the hydraulic cylinder 1 whichare associated with the preceding FIGS. 7 and 8, the excursion values dXof the support bearing 7 and the spring compression Xe. The supportbearing 7 which, according to the invention, is coupled hydraulically tothe hydraulic cylinder 1 carries out a large number of the springcompression movement in this operating case. The transitions to theactual hydraulic cylinder excursion values Xz take place harmonicallyand smoothly. Uncertainties with respect to the level of frictionalforces play virtually no role and fluctuations in frictional force wouldmerely shift somewhat the times when the cylinders are moved but notdisrupt the continuous transitions when there is a reversal of movement.

FIG. 10 illustrates a further preferred configuration of a supportbearing 7 according to the invention. With the configuration of thesupport bearing 7 it is particularly expedient to provide as littleaxial rigidity of the support bearing 7 as possible and at the same timeto permit no or only slight changes in the hydraulic effective areaA_(L) during the spring compression and extension. For this purpose, thesupport bearing 7 can have a housing 10 which is formed from anelastomer at least in certain areas. The housing 10 may preferably beattached directly to the hydraulic cylinder 1 and to a force absorbingmeans 9. For this purpose, a clamping ring 11 may be provided with whichthe housing 10 is secured directly to the housing of the hydrauliccylinder 1. Furthermore, it is possible to provide a correspondingsecuring means 12, for example a clamping ring, by means of which thehousing 10 is attached to the force absorbing means 9. A perforateddiaphragm 8 may be provided for the hydraulic cylinder 1. The opening ofthe perforated diaphragm 8 forms the hydraulic effective area A_(L).

The force absorbing means 9 is connected, for example, to the body of avehicle using a bearing point 13.

The housing 10 is particularly preferably composed of a rubber cylinderwhich forms the actual bearing element. The rubber itself gives rise tolongitudinal flexibility in the direction h of the support bearing 7. Afavorable compressive strength and sufficient radial rigidity in thedirection b can be produced by means of tangential, or at least almosttangential, reinforcing fibers in or on the rubber cylinder. Given anappropriately favorable configuration is possible for the rubbercylinder itself also to perform lateral guidance functions of thesupport bearing 7. If relatively high lateral forces are transmitted orrelatively stringent requirements are made in terms of the precision ofthe lateral guidance it is possible to introduce correspondinglongitudinal guide means.

One favorable configuration of the support bearing 7 is illustrated inFIG. 11. The arrangement corresponds essentially to that in FIG. 10. Inaddition, a rod 14 is provided in the housing 10 and is oriented axiallywith respect to the hydraulic cylinder and can project into thehydraulic cylinder. A compression stop 15 and/or an extension stop 15may be provided on the rod 14. As a result, the maximum compressionand/or extension of the support bearing 7 can be limited or adjusted.

A further favorable configuration of the support bearing 7 isillustrated in FIG. 12. A longitudinal guide means 18, which limits orprevents lateral excursion of the support bearing 7, is provided on therod 14. The longitudinal guide means 17 may be a cylinder whichsurrounds the rod concentrically. On the underside the cylinder widensin the direction of the perforated diaphragm 8 and preferably includes aring 18. In the perforated diaphragm 8 overflow openings whose crosssections form in total a hydraulic effective area A_(L) are expedientlyprovided. The ring 18 can also be arranged on the side of the supportbearing 7 which faces the force transmission means 9.

Other configurations of a support bearing which is hydraulically coupledto a hydraulic cylinder 1 are, of course, also conceivable.

The invention is defined by the fact that the support bearing 7according to the invention is not subjected to the high static loads tobe borne, but those loads are hydraulically directly transmitted to theforce transmission means, that is, to the vehicle body. This permits“soft” construction and, for example, the use of elastomers.

It is very particularly advantageous if the support bearing 7 forms ahead bearing of a hydraulic cylinder 1. It is particularly favorable toconfigure the overall rigidity of the support bearing 7 in such a waythat when there is spring compression or spring extension the change inforce by means of an available excursion in the support bearing 7 isgreater than the frictional force, in particular the static frictionalforce of the piston 6 in the hydraulic cylinder 1. This ensures that thepiston 6 can tear out of a frictionally clamped position again beforethe support bearing 7 strikes against its excursion limits. Thenecessary rigidity can be provided either solely by elastic materialproperties of the support bearing 7 or of the housing 10 or additionallyor alternatively by a change in area of the hydraulic active area A_(L)over the spring compression travel. Both act in a comparable fashion ifthe overall rigidity has been configured according to the conditionmentioned above.

1. A shock absorber support arrangement including a support bearingstructure (7), a piston (6) in a hydraulic cylinder (1) which is coupledhydraulically to the support bearing structure (7), the support bearingstructure (7) having a housing (10) which is filled completely with ahydraulic medium, the housing (10) being formed at least in certainareas by one of an elastomer cylinder and a folding bellows, and ahydraulic effective area (A_(L)) being arranged between the hydrauliccylinder (1) and support bearing structure (7), which remainsessentially constant under the excursion of the hydraulic cylinder (1)and the support bearing structure (7), said hydraulic bearing structure(7) being resilient and connected to the cylinder (1) so as to permitaxial movement of the hydraulic cylinder as a result of friction forceseffective between the piston (6) and the hydraulic cylinder (1).
 2. Ahydraulic shock absorber support arrangement as claimed in claim 1,wherein the hydraulic cylinder (1) is connected to a gas springaccumulator (2) via an overflow line (4) for a hydraulic medium.
 3. Ahydraulic shock absorber support arrangement as claimed in claim 2,wherein the support bearing structure (7) is arranged hydraulically inparallel with the gas spring accumulator (2).
 4. A hydraulic shockabsorber support arrangement as claimed in claim 1, wherein a hydrauliceffective area (A_(L)) is arranged between the hydraulic cylinder (1)and the support bearing structure (7) and remains essentially constantunder excursion of the hydraulic cylinder (1) and the support bearingstructure (7).
 5. A hydraulic shock absorber support arrangement asclaimed in claim 4, wherein the hydraulic effective area (A_(L)) isapproximately equal to an effective working area of the hydrauliccylinder (1).
 6. A hydraulic shock absorber support arrangement asclaimed in claim 1, wherein the support bearing (7) is formed by ahousing (10) which is filled with the hydraulic medium.
 7. A hydraulicshock absorber support arrangement as claimed in claim 6, wherein aseparate force transfer means (9) is arranged between the housing (10)and a coupling point (13) for the support of the body of a vehicle.
 8. Ahydraulic shock absorber support arrangement as claimed in claim 6,wherein the housing (10) is formed by a folding bellows, at least incertain areas.
 9. A hydraulic shock absorber support arrangement asclaimed in claim 6, wherein the housing (10) is formed by an elastomercylinder, at least in certain areas.
 10. A hydraulic shock absorbersupport arrangement as claimed in claim 1, wherein the housing (10) isdirectly connected to the hydraulic cylinder (1).
 11. A hydraulic shockabsorber support arrangement as claimed in claim 1, wherein the supportbearing structure (7) has at least one of an extension stop (16) and acompression stop (15).
 12. A hydraulic shock absorber supportarrangement as claimed in claim 1, wherein the support bearing structure(7) includes a longitudinal guide member (17).
 13. A hydraulic shockabsorber support arrangement as claimed in claim 1, wherein a perforateddiaphragm (8) is arranged between the hydraulic cylinder (1) and thesupport bearing structure (7).
 14. A hydraulic shock absorber supportarrangement as claimed in claim 1, wherein of the support bearing (7) isconfigured with an overall rigidity such that when spring extension orspring compression occurs the force change in the support bearingstructure (7) is greater than the frictional force of the piston (6) inthe hydraulic cylinder (1).
 15. A hydraulic shock absorber supportarrangement as claimed in claim 1, wherein the support bearing structure(7) has a mechanical spring stiffness (C_(L)) which is less than 50N/mm.
 16. A hydraulic shock absorber support arrangement as claimed inclaim 1, wherein the support bearing structure (7) forms a head bearingof the hydraulic cylinder (1).
 17. A hydraulic shock absorber supportarrangement as claimed in claim 1, wherein the support bearing structure(7) is a head bearing of a hydropneumatic spring damper.